1) Field of the Invention
The present invention relates to a process for producing alkylbenzoyl chloride by chlorination of alkylbenzaldehyde. Alkylbenzoyl chlorides have been widely used in various fields as starting materials or intermediates for agricultural chemicals, chemical synthetic products, etc.
2) Prior Art
Hitherto, as a process for producing benzoyl chlorides, it has been regarded that the process for producing benzoyl chlorides by hydrolysis of the corresponding benzotrichloride is economical.
On the other hand, a process which comprises chlorinating alkylbenzene carboxylic acid as a starting material with a chlorinating agent including thionyl chloride, phosphorus pentachloride, etc., thereby producing the corresponding acid chloride, a process for producing benzoyl chloride by the reaction of benzaldehyde having no alkyl side chain with chlorine (U.S. Pat. No. 3,894,923), etc., are known.
Among the processes, in the process for producing alkylbenzoyl chloride by hydrolysis of the corresponding alkylbenzotrichloride, alkylbenzotrichloride as a starting material is indispensable. In order to obtain alkylbenzotrichloride, only one methyl group on alkylbenzene having at least two alkyl-substituted groups need to be selectively chlorinated. Thus, it is very difficult to carry out selectively such reaction.
Moreover, in the process for chlorinating alkylbenzene carboxylic acid with thionyl chloride, etc., the yield of acid chloride is high, but the use the chlorinating agent is more expensive than that in case of chlorine being used as starting material and causes many problems in purification and post treatment.
On the other hand, in the process for producing benzoyl chloride by reacting benzaldehyde with chlorine, benzoyl chloride can be obtained in a high yield. Therefore, the process is very excellent as a process for producing benzoyl chloride having no alkyl-substituted group. However, in the reaction alkylbenzaldehyde having an alkyl side chain(s) as starting material with chlorine, it is difficult to obtain the corresponding alkylbenzoyl chloride in a high yield. No industrial process for producing alkylbenzoyl chloride is known because alkyl group as side chain in alkylbenzaldehyde readily reacts with chlorine. Thus, by the reaction of alkyl group with chlorine, side chain chloride of alkylbenzaldehyde as the starting material and side chain chloride of the intended alkylbenzoyl chloride, etc., are readily by-produced in a large amount and the yield of the intended alkylbenzoyl chloride often markedly deteriorates. Furthermore, since the boiling point of the intended alkylbenzoyl chloride is close to that of by-products, the separation by distillation is difficult, so that problems in purification occur.